Low oxygen-silicon base addition alloys for iron and steel refining



Feb 14, 1967 Tom-:l oToTANl ETAL 3,304,174

Low OXYGEN-SILICON EASE ADDITION ALLOYS FOR IRON AND y STEEL EEEINING Filed Aug. l?, 1964 2 Sheets-Sheet l o case @Casual F11-6l' (www aan' United States Patent Filed Aug. 17, 1964, Ser. No. 389,833 3 Claims. (Cl. 75-122) The present invention relates `to low oxygen-silicon base addition alloys for iron and steel characterized in that they contain 5-0 to 97% silicon, 0.1 to 30% manganese, 0.1 to calcium and the remainder iron, the oxygen content being less than 0.04%.

The object of the invention is to improve the properties of refining alloys such as the refining effect and economical problems as compared with those of conventional Fe-Si, Ca-Si, Ca-Si-Mn, Fe-Si-Mg alloys and misch metal.

The refining alloys mentioned above have heretofore been used for the removal of oxygen, sulfur and other impurities in case of casting iron, steel and non-ferrous alloys, or for the graphitization of high carbon steels after elimination of impurities or for improvement of the graphite form in cast iron.

The compositions of the refining alloys by the present invention are shown in Table 1 as an example, wherein the number is shown in weight percent.

As shown in Table 1, the oxygen content in the alloys is less than 0.04%. On the other hand, the inventors have found that the oxygen content in conventional Fe-Si alloys and other Si alloys is more than 0.04% in almost all alloys. The oxygen content in such cases was ascertained by the analysis of oxygen by a vacuum fusion method or by calculation from the analysis val-ue of oxide.

The other elements listed in Table 1 are elements entering mainly in the manufacturing steps, such as C, Cr, Cu, Ni, P, S, T e, Na, Mg, K, Ti, Y, Li, Zn, Zr, lanthanum series elements (rare earth elements).

The reason why the oxygen content is limited to be less than 0.04% as one of the characteristics of the invention is based on the fact that it limits the oxide content in the alloy and improves the activity of elements having the refining action such as Si, Mn and Ca and also increases their affinity with oxygen and other impurities in the melt.

For a lbetter understanding of the invention, reference is taken to the accompanying drawing, in which,

FIG. 1 shows curves illustrating the test results of the deoxidizing action taken for comparison of usual Fe-Si alloy (75% Si) with the alloy of the invention having similar composition thereto,

FIG. 2 shows curves illustrating the relation between the oxygen content in the Fe-Si addition alloy and that in the cast iron treated with the addition alloy and the tensile strength of the cast iron at as-cast state, and

ice

FIGS. 3 and 4 are equilibrium diagrams of SiOZ-MnO system (White-Howat-Hay) and SiOz-CaO system (Shepherd-Rankin, Ferguson-Merwin) respectively illustrating that the oxides produced by using the alloys of the invention are mainly complex system of SiO2-MnOCaO series.

After fundamental experiments the inventors have ascertained as shown in FIG. 1 that there is `a great difference between the deoxidizing action of conventional Fe-Si alloy Si) and the invented alloy which has a similar composition except oxygen to conventional Fe-Si alloy.

In FIG. l, the curves illustrate the relation between the added amounts and the oxygen contents in cast irons after the addition of these alloys. The composition of the cast iron before the addition of the alloys was 3.2% C, 0.1% Si, 0.2% Mn, 0.0025% O2, and the remainder Fe. The composition -of the alloys used for the experiments is as follows:

COMPOSITIONS OF TESTED ALLOYS As shown in FIG. 1, when a conventional Fe-Si alloy of high oxygen content is added in 1 to 2% to the molten pig iron, the oxygen content in the cast iron is reduced slightly, but the oxygen content in the cast iron increases reversely with increase of the addition in excess of 3%.

This phenomenon is due to the fact that the oxide (mainly S102) in the Fe-Si alloy is brought into the cast iron melt and a part of which is suspended in the melt without flotation. Even if Fe-Si alloy containing `a large amount of oxide is added to the molten cast iron, the quantity of the soluble oxygen should be reduced by silicon. However, the oxygen content in cast iron is increased due t-o the introduction of oxide is so much larger than the reduced amount of soluble oxygen.

On the contrary, when the low oxygen content alloy of the invention is added, the oxygen content in the cast iron is reduced considerably as go with the addition increases (FIG. 1).

As shall be mentioned later, the remarkable deoxidizing effect in the use of alloys of the invention is also due to the formation of fioatable oxides, chiefly, the SiOz-MnO-CaO system, in molten iron or molten steel by addition of the alloy containing Mn and Ca besides Si.

The inventors have made experiments on 12 kinds of the conventional and invented Fe-Si alloys which have low contents of Mn, etc. elements except Fe and Si by adding each 3.5% to the cast iron having a definite composition, and determined the relation between oxygen content in the added Fe-Si alloy `and the as-cast tensile strength of the added cast iron. The reason why cast iron was taken for the experiments is due to the fact that the deoxidized extent is expressed as the variation in the shape of graphite and it depends on the as-cast tensile strength,

The experimental results are shown in FIG. 2.

Experimental conditions (A) Composition of Fe-Si alloy samples:

(B) Composition (percent) of cast iron before addition of the Fe-Si alloy:

(C) Temperature of the cast iron melt in case of the Fe-Si alloy addition: 1,45 C.

As shown in FIG. 2 the oxygen content of the Fe-Si alloy was limited to 0.04% as the reference point and less than it the deoxidizing effect became more powerful 'and over than it the deoxidizing effect `become reduced. Such effects influence the tensile strength: If the oxygen content of cast iron is lower, the tensile strength becomes higher, but with increase of the oxygen content, the tensile strength is reduced. In this test, the relation between the tensile strength of the cast iron and the shape of graphite was investigated with the following results:

Tensile strength, Shape of graphite: lig/mm.2

Spheroidal graphite only 68 Spheroidal graphite and wormy fiake graphite 53 to 61 Wormy flake graphite and flake graphite 27 to 31 Flake graphite 'only 2l to 23 From the results of the above experiments the inventors have confirmed the importance of the oxygen content in the silicon base alloys and further that the oxygen content in the alloy should be less than 0.04% in order to obtain a remarkable refining effect. Moreover, the large refining effect of the alloy of the invention is not only based on the oxygen content less than 0.04%, but `also on the contents of Mn and Ca besides Si.

As already explained, the inventors have noticed that in molten steel or molten cast iron SiOZ or silicate is suspended and hardly floatable. The oxides produced by the use of the alloy of the invention forms mainly Aa complex system of SiO2MnO-CaO, andas given in FIGS. 3 and 4, they have low melting points and make floatable. FIG. 3 represents an equilibrium diagram of the SiOg- MnO system and FIG. 4 that of the SiOZ-CaO system.

The principal reason for addition of Mn and Ca ybesides Si to the alloy of the invention is to facilitate the flotation of the oxide produced and to exhibits the cooperating reaction in the ,refining activities of Si, Mn, Ca and Mg.

The reason why Si is made the chief component ac-v counting for more than 50% in the composition of the alloy of the invention is based not only on the consideration of the refining effect of the alloy but also on Ithe fact that Si is in the widest use in the iron and steel refining and is an inexpensive metal and also the alloy can he manufactured easily. The Si content of the alloy of the invention can further be increased when the contents of Mn, Ca, and Fe are low, but the upper limit is 97% since in the high silicon alloy of the invention, simil-ar to the conventional metallic silicon, the refining effect requires the total sum of the contents of Mn and Ca to be more than about 3%. The Mn content was limited within the range of 0.1 to 30% preferably 0.1 to 10%.

The lower limit of the Mn content is fixed to be 0.1%, as it is the minimum quantity necessary for producing the oxide of the above-mentioned complex system. The upper limit of 30% is based on the fact that the addition of more than it reduces the refining effect due to lthe cooperating reaction with .the other elements. This is probably due to the lower affinity of Mn with `oxygen than Si and Ca. The Ca content was limited within the range of 0.1 to preferably 0.1 to 7%.

The lower limit of Ca is selected to be 0.1% as it is the minimum quantity necessary for developing the refining effect due to having affinity with impurities and the forma-tion of the floatable oxide.

The upper limit is determined to be 10%, since with the Ca content higher it only increases the manufacturing cost and no improvement is brought labout in its refining effect. The alloy of the invention which is lower in the Ca content than conventional Ca-Si alloys yand Ca-Si-Mn alloys, but it exhibits a more powerful refining effect than the latter alloys due mainly to its low oxygen content.

The oxygen content was limited below 0.04% due to the reason that more than it the oxides of Fe, Si and Ca are not only increased as described above but also the activities of these elements are reduced so that the reflning effect as desired by the invention can not be attained. The impurities which enter unavoidably during the manufacturing process of the alloy of the invention are C, Cr, Cu, Ni, P, S, Te, Na, Mg, K, Ti, Y, Li, B, Zn, Zr, lanthanum elements, H2 and N2. Among these elements there are two metallurgically known classes of elements which act positively for the refining action of iron and steel such as Te, Na, Mg, K, Ti, Y, Li, B, Zn, Zr, and lanthanum elements (rare earth elements)` and also the elements acting negatively such as H2, P and S. The rate of entering these elements differs according to the method of manufacturing their alloys, but in any process the quantity of elements positively acting for the refining action is in most cases equal to or larger than that the quantity of elements acting negatively. It has been found that even if the refining effects of both of these elements are compensated, the total sum of these elements up to maximum 6% does not disturb the refining action attainable by the `alloy of the invention. In the manufacture of the alloy of the invention, the lowering of the oxygen content necessitates higher temperature smelting than in the case of manufacturing conventional Fe-Si alloys. The high temperature smelting is not only to make the reduction of oxides in raw material easier but also it makes more perfect separation of molten alloy and slag. It is also usual in manufacturing the alloy of the invention to add lime stone besides silica as the raw material. Moreover, in manufacturing alloy of the invention these is ya method of heating or remelting the Fe-Si alloy manufactured by a conventional process and adding Mn and Ca during its step. In adding Mn and Ca there are two different methods: (l) The direct addition of these metals or alloys; (2) The addition of these metals by the reduction of oxides of such elements in slag. The refining alloys of the invention can be used for the melting of various kinds of metals and alloys, among which a remarkable refining effect has been obtained for steel for construction, high silicon steel, stainless steel, tool steel, graphitic steel, stainless cast steel, graphite cast steel, tough cast iron and spheroidal graphite cast iron. The invention will be explained in detail by examples in use.`

Example 1 No Nomenclature i Si Mn i Ca O Fe Othels 1 Ca-Si-Mn 61.1 15.2 20.8 0.52 1.4 0.98

2 Alloy ofthe inven- 62.5 12.4 7.2 0.028 14.7 3.172

tion.

(2) Refining effect (test results of stainless steel products):

' Analyzed Non-metallic inclusion by Name oi composition JIS-Standard (Percent) addition (percent) No. alloy for refining Sullide Alu- Granu- S O and mina lar Total silicate oxide 1 Ca-Si-Mn 0. 012 0. 0049 0. 014 0. 008 0. 0044 0. 0006 2 Alloy 01' the 0. 004 0. 0019 tx'. tr. 0. 0020 0` 0020 invention.

NoTE.-In the table, JIS means Japanese Industrial Standard.

6 As shown in Table 2, t-he allowable maximum S-content in the molten cast iron increases as the contents of Mn and Ca in the addition alloy increase. This depends on the desulfurization effects of Mn 'and Ca in the alloy.

Example 3 Analyzed compositions (percent) Tensile Duration of Kinds 0i addition alloys for refining strength Elongation spheroidal (kg/mm1!) (percent) graphiti- C Si Mn S O zation No. 1 alloy in Table 2 3. 54 2.83 0. 27 0.011 0.0008 65.9 2.4 12 Alloy of the invention SC N o. 3 in Table 1 3. 41 2. 78 0. 35 0. 005 0. 0004 74. 8 4. 8 25 As compared the compositions of the above two alloys, the invented one is about 3% and 14% lower in the Mn and Ca contents respectively than those of Ca-Si-Mn alloys, notwithstanding the refining action of the alloy of the invention which is more powerful.

Example 2 The inventors ascertained several years ago that when Fe-Si alloys of low oxygen content were used, spheroidal graphite cast iron could be manufactured by the addition of Fe-Si alloy only, but in the method of adding Fe-Si'alloy only, if the sulfur content in the molten cast iron before addition of the alloy was considerably high, the spheroidal graphitization was not perfect. On the other hand, if the alloy of the invention is used, satisfactory spheroidal graphite cast iron can be obtained even from molten cast iron having unfavorable conditions by the effective refining effect of a small quantity of Mn and Ca.

As apparent from the above results, the alloy of the invention has not only a powerful effect of graphite spheroidization but is also very effective to elongate the duration of graphite spheroidization. In the melting of spheroidal graphite cast iron, the longer the time from the addition, of the refining alloy to the casting in a mold beyond a certain limit, the lower is the rate of graphite spheroidization. The duration time of graphite spheroidization represents the interval from the instant when the alloy is added into the ladle to the time when graphite spheroidization begins to decrease.

Example 4 steel scrap and 50% returned scrap were used as the raw material and melted in a 1.5 ton basic Hroult arc funnace, to which 1.2% alloy (SC3 in Table 1) of the invention was added. The spheroidal graphite cast steel thus produced shows the following composition and properties.

Analyzed compositions (percent) as-cast condition Properties after annealed NOTE-In the tabl before the addition of the alloy, 0.022%;

TAB LE 2 Compositions percent of addition alloys Allowable max. No. content of S in molten pig iron O Fe Others Nora-In the table, No. 1 alloy does not belong to the invention.

Tensile Elongation T. C. G.C. Si S O G. C strength (percent) (kg./n1n1.2)

e, T C. means total carbon; G.C., graphite carbon;

the Seontent the O-content, 0.0048%.

The deposition of 0.48% graphite carbon under the as-cast state is due to the refining activity of strong deoxidation and desulfurization effects of the addition alloy of the invention.

Example 5 It is generally known that in the manufacture of tough cast irons, oxygen and sulfur are extensively dispersed in lots and the oxygen content in the inoculation alloy is high so that it is diliicult to obtain the product having a definite quality.

However, even under the worst condition when molten cast iron in an acidic cupola is used, it becomes possible to manufacture the product of a definite quality by the use of the alloy of the invention. 35% pig iron, 35% returned scrap and 30% steel scrap were used as the raw material and melted in a 2 tons cupola, to which 0.6% alloy of the invention (SMCI in Table 1) was inoculated.

ANALYSIS OF THE PRODUCTS AND TEST RESULTS 2. A low oxygensi1ic0n base addition alloy for rening iron and steel according to claim 1, wherein the man- Analyzed composition (percent) Tensile 31165@ COHSH S 0-1 O 10%- BIOWNO- 3. A 10W oxygen-silicon base addition alloy for refin- C Si O 5 ing iron and steel according to claim 1, wherein the calcium content is 0.1 to 7%.

. .o 3 .4 3.16 2.16 0. 0030 32. 5 References Cited by the Examiner e. 33 2. 0G 0. 0022 35. 6 2 1'97 0 0019 3&6 10 UNITED STATES PATENTS what We Claim is: 2,950,187 8/1960 OtOtani 75-123 X 1. Low oxygen-silicon base addiion alloys for reng ing iron and steel consisting essentiaily of 50 to 97% sili- DAVD L- RECK: Pnmmy Examiner' con, 0.1 to.30% manganese, 0.1 to 10% calcium and the 15 P. WETNSTEIN Assistant Examine. remainder iron, the oxygen content being less than 0.04%. 

1. LOW OXYGEN-SILICON BASE ADDITION ALLOYS FOR REFINING IRON AND STEEL CONSISTING ESSENTIALLY OF 50 TO 97% SILICON, 0.1 TO 30% MANGANESE, 0.1 TO 10% CALCIUM AND THE REMAINDER IRON, THE OXYGEN CONTENT BEING LESS THAN 0.04%. 